This is important because (a) if you didn't mean to mutate state that's *bad* and (b) by altering the semantics of what intermediary forms of the computation are required you've changed the result of the floating point calculation quite a bit.

you should also be aware that the sort of calcualtions you're describing are ripe for an optimising compiler to tweak the hell out of, so the low order bits of precision should be viewed as containing very little useful information. If you have extreme differences in the values of various numbers involved in the calculation (squaring very big or very small numbers can do that) then this goes double <ahem>

Also never describe mathematical operations and snippets without describing the data types in question (and for FP the compiler toolchain/options & hardware used often matters a great deal)